1. Field of the Invention
The present invention relates to a camera and, more particularly, to a camera including an oscillating pupil autofocus device.
2. Description of the Related Art
Photographic film cameras are known which employ optical sensing devices for detecting and controlling focus. In general, these cameras include not only traditional optics and film handling mechanisms for the film, but also include additional optics and some type of solid state imager or photosensitive device to view an image of the scene. In the case of the solid state imager, an electronic image can be used to preview the scene for a variety of purposes, including focusing, before exposing the film.
In cameras employing solid state sensors, the same components of the optical system needed to produce an image of the scene are generally used to determine focus, exposure, and other data. However, for focus detection, the cameras employ a contrast method. With the contrast method, the contrast of an image of the scene when the lens aperture is wide open is compared to the contrast of the image when the lens aperture is stopped down. If there is a focus error, there is no indication of its direction. As a result, the lens must be moved in one of two directions and the error checked again to see if the focus improved. A disadvantage of not knowing the focus error direction frequently requires extra lens travel time. The use of extra lens travel time is undesirable in a camera application, since a subject may move during the extra lens travel time, resulting in a missed photographic opportunity.
Another type of known camera autofocus device employs an oscillating pupil technique. In general, some type of special mask is required to alternately obstruct different portions of an optical system to form images of the object. The presence of either a stationary or moving image is indicative of the focus condition of the optical system. A major disadvantage of such known oscillating pupil devices in cameras is the requirement of a special masking means and/or the requirement of additional focusing optics, in addition to the main camera optics.
For instance, in U.S. Pat. No. 4,201,456, issued May 6, 1980, a special mask is employed for alternately obstructing different portions of the camera optical system for detecting its focusing condition. A disadvantage of the '456 device is the requirement of the special mask in addition to the traditional camera optical components. Likewise, U.S. Pat. No. 3,833,806, issued Sep. 3, 1974, discloses an automatic focus control circuit which employs a special vibrating slit in addition to the traditional optical components of the camera.
Other known oscillating pupil focusing devices are disclosed in U.S. Pat. No. 4,543,476, issued Sep. 24, 1985; U.S. Pat. No. 4,631,394, issued Dec. 23, 1986; U.S. Pat. No. 4,740,678, issued Apr. 26, 1988; U.S. Pat. No. 4,833,315, issued May 23, 1989; U.S. Pat. No. 2,999,436, issued Sep. 12, 1961; U.S. Pat. No. 3,906,219, issued Sep. 16, 1975; and U.S. Pat. No. 3,941,996, issued Mar. 2, 1976. The major disadvantage of these devices is that each requires the use of a special mask and additional focusing optics. This adds cost, takes up additional space, and adds complexity to an overall camera device. These disadvantages are undesirable in low cost, compact, autofocus camera applications.
It would thus be desirable to provide oscillating pupil autofocus capability to a camera in which minimal additional components are required, compactness is maintained, and any added complexity to the overall camera design is minimized.